1. Field of the Invention
The invention relates to an oil pressure supply device, and more particularly, to an oil pressure supply device having an oil pump for supplying an oil pressure to an oil passage from a plurality of ports.
2. Description of the Related Art
There is known a vehicle mounted with a hydraulically actuated transmission. An oil pressure used to actuate the transmission is supplied from an oil pump. The oil pump is driven by, for example, an engine. Accordingly, when the amount of oil discharged from the oil pump is large, the amount of energy loss is correspondingly large. On the other hand, when the amount of oil discharged from the oil pump is small, the oil pressure needed to actuate the transmission is insufficient. Thus, there is proposed an oil pressure control device having an oil pump with a plurality of ports for discharging oil to allow the amount of oil discharged from the oil pump to be changed.
Japanese Patent Application Publication No. 3-213773 (JP-A-3-213773) discloses an oil pressure control device of a continuously variable transmission that is capable of changing the amount of oil from an oil pump. The oil pressure control device described in Japanese Patent Application Publication No. 3-213773 (JP-A-3-213773) has at least a plurality of discharge ports. All but one of the discharge ports are equipped with check valves and/or solenoid valves respectively. The oil pressure control device includes an oil pump capable of selecting load operation or no-load operation, and a control unit for comparing a required amount of oil in the continuously variable transmission, a torque converter, and the like with a total amount of oil in the pump, selecting one or more of the discharge ports to be operated under a load, and outputting a selection signal to each of corresponding ones of the solenoid valves.
According to the oil pressure control device described in this Japanese Patent Application Publication No. 3-213773 (JP-A-3-213773), the plurality of the discharge ports of the oil pump are selectively operated under a load. Therefore, the amount of oil in the pump can be constantly made appropriate, namely, coincident with the required amount of oil.
However, the oil pressure control device described in Japanese Patent Application Publication No. 3-213773 (JP-A-3-213773) is provided with the dedicated solenoid valves for allowing the discharge amount of the oil pump to be changed. Therefore, there is a problem in that the number of parts increases.